In machines for automatically processing mail, an envelope unstacker at the outlet from a magazine of envelopes serves to take envelopes one by one from the magazine. A transfer device for transferring empty envelopes transfers the separated empty envelopes to an insertion station for inserting sheets into said envelopes.
At the insertion station, successive envelopes are stopped and held open. The sheets to be put into the envelopes (which sheets may be in the form of single sheets or in the form of bundles of sheets) are folded appropriate in a folding machine and are optionally made up into bundles by a bundling machine either before or after folding, and are then delivered in succession to the machine for processing mail.
A sheet transfer device or an insertion device per se transfers successive sheets that it receives and inserts them into respective envelopes at the insertion station. An ejection device for ejecting filled envelopes ensures that each filled envelope is removed so that a new insertion operation can take place.
Control mechanisms control these various devices to operate synchronously. In order to satisfy current requirements, these control mechanisms must be capable of operating at high insertion rates with the various devices all operating with a high degree of reliability.
French patent document No. FR 84 14141 in the name of the present Applicant and entitled "A device for inserting a bundle into an envelope" already describes a device for inserting each sheet that it receives into the envelope which is then present in the insertion station.
In this prior device, a sheet feed path for feeding separate sheets to be put successively into envelopes feeds a fixed sheet inlet station. This sheet feed path includes a fixed sheet-receiving tray which extends the sheet feed path and which is disposed at a distance from and substantially level with the insertion station. A serving tray which is mounted to move back and forth and which is referred to as a carriage serves to transfer successive sheets from the fixed inlet station to the insertion station, and to insert them into the envelopes. The carriage is driven along its "go" stroke and its "return" stroke between two limit positions, referred to as a "rest" position in which it is beneath the inlet station and a "working" position in which it is partially engaged together with the sheet carried thereby inside the envelope present at the insertion station. Retractable pusher fingers are linked to the carriage and they form both an abutment for the sheet which they push during the "go" stroke of the carriage, and a retracted obstacle for the following sheet to be put into the next envelope during the "return" stroke of the carriage.
These retractable fingers are mounted on parallel support arms carried by the carriage and extending between the level of the inlet station and the level of the carriage. They are linked to the support arms by individual hinges leaving a degree of longitudinal play along the support arms. They are also coupled to the carriage and associated with means for causing them to move in translation along said longitudinal play on their corresponding support arms in one direction and the other direction on passing from the "go" stroke to the "return" stroke and vice versa, and they are put simultaneously into the raised position or into the retracted position i.e. to constitute an abutment for the sheet currently being inserted or a retracted obstacle for the following sheet to be put into the next envelope, depending on the direction of the current stroke, of the carriage.
Such an insertion device having retractable pusher fingers which are put into a raised position during the "go" stroke of the carriage provides reliable engagement with a sheet present at the inlet station for insertion into an envelope. These same pusher fingers, when retracted for the "return" stroke of the carriage enable a new sheet to arrive at the inlet station while the preceding sheet is being transferred and during the "return" stroke of the carriage. They thus contribute to obtaining a very high insertion rate. However, they increase the complexity of the insertion device and the complexity of its control mechanisms, thereby considerably increasing the cost of a sheet insertion device.
The object of the present invention is to simplify such an insertion device and consequently to reduce its cost, but without thereby loosing the advantages of high insertion rates being possible with a high degree of operating reliability.